Definition

Spinocerebellar ataxias (SCA) are a genetically heterogeneous group of diseases characterized by progressive cerebellar ataxia, most commonly caused by abnormal CAG trinucleotide repeat expansions in the coding regions of the related genes. Standard panel testing measures the repeat number in the ATXN1 (SCA1), ATXN2 (SCA2), ATXN3 (SCA3), CACNA1A (SCA6), and ATXN7 (SCA7) genes; as the repeat number increases, the disease tends to appear at an earlier age (anticipation).

Gene/region examined

SCA-1, SCA-2, SCA-3, SCA-6, SCA-7, SCA-8, CAG, CTA/CTG

Method

Fragment analysis

Accepted sample types

EDTA blood

Inheritance

Inherited, mostly autosomal dominant (varies by type and gene).

Related Tests

Inheritance Patterns

Describes how a genetic condition is passed on within a family. There are five main patterns

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Carrier (Heterozygous / Homozygous)

Why it matters: In autosomal recessive inheritance, when each parent is a carrier (while both appear healthy), the chance of their child being born with the disease is 25% in each

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VUS (Variant of Uncertain Significance)

This is the situation where the test has detected a change in the DNA, but the role of this change in the development of disease is unconfirmed.

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How to Read a Genetic Test Result (Positive / Negative / VUS)

A genetic test result falls into three main categories

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Types of Genetic Tests

A genetic test is a type of medical test that detects changes in genes, chromosomes or proteins. Today there are more than 77,000 genetic tests available.

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